Gas-filled electric discharge device with improved recovery



July 29, 1969 FRASER ET AL 3,458,758

GAS-FILLED ELECTRIC DISCHARGE DEVICE WITH IMPROVED RECOVERY Filed Oct. 26, 1965 I 5 Sheets-Sheet 1 IMVGN DR'S Dav/D LEXHMDE EHSER 014v Gowmz 4,4,2, am. a 9

f YS July-29, 1969 D, A, FRASER ET AL 3,458,758

GAS-FILLED ELECTRIC DISCHARGE DEVICE WITH IMPROVED RECOVERY Filed Oct. 26, 1965 a Sheets-Sheet 2 Fig. 2

INVENTORS l p FILCMNDE 5 2 JOHN Gown-R H'T' OR NeYs July 29, 1969 b, A FRASER ET AL 3,458,758

GAS-FILLED ELECTRIC DISCHARGE DEVICE WITH IMPROVED RECOVERY Filed Oct. 26, 1965 r a Sheets-Sheet a Pu\se Voltage AB Source 24 T19 T 1 ig 52 l I H/HII 1 A&\\\

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aw; F/u-xnAmaa 9592 nv Go l HTIW'OR YS United States Patent 3,458,758 GAS-FILLED ELECTRIC DISCHARGE DEVICE WITH IMPROVED RECOVERY David Alexander Fraser, Edgware, and John Gowar, Pinner, England, assignors to The M-() Valve Company Limited, London, England Filed Oct. 26, 1965, Ser. No. 505,275 Claims priority, application Great Britain, Oct. 24, 1964, 43,873/ 64 Int. Cl. Hb 39/04, 41/14; H01j 13/28, 17/22 US. Cl. 315-102 6 Claims ABSTRACT OF THE DISCLOSURE A gas-filled electric discharge device having a planar metal electrode, which may be negatively biassed during the recovery period to reduce recovery time, and whose surface, except in the region(s) of one or more apertures in the electrode through which the main discharge passes in operation, is screened from the discharge by two correspondingly apertured planar metal members between which said electrode is positioned in parallel close-spaced relation.

This invention relates to gas-filled electric discharge devices.

The invention relates particularly to gas-filled electric discharge devices of the kind comprising an anode, a cathode and a further metal electrode having at least one aperture through which the discharge between anode and cathode passes in operation, and to which a negative potential with respect to the cathode may be applied during a period immediately following the interruption of a discharge between the anode and the cathode so as to reduce the recovery time of the gap between the anode and cathode of the device.

It is an object of the present invention to provide a gasfilled electric discharge device of the kind specified wherein the current drawn from a voltage source supplying said negative potential in operation is reduced.

According to the present invention, in a gas-filled electric discharge device of the kind specified, said further electrode comprises a planar metal member disposed in parallel spaced relation between, and insulated from, two further parallel planar metal members each having at least one aperture through which the discharge -between anode and cathode passes in operation, said further members together serving to limit the surface of said further electrode which is exposed to said discharge to the region(s).immediately adjacent the aperture(s) in said further electrode.

Two gas-filled devices in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIGURES 1 and 2 are respectively cross-sectional views of the two devices;

FIGURE 3 is a circuit diagram illustrating a typical ap lication of the device shown in FIGURE 1; and

FIGURES 4 and 5 illustrate modified forms of the device shown in FIGURE 2.

Referring to FIGURE 1, the first device to be described is a hydrogen-filled thyratron having a sealed, hollow, generally cylindrical, glass envelope 1 in which is housed an electrode structure including an indirectly heated cathode 2, a control electrode arrangement 3, and an anode 4.

The cathode 2 is of hollow cylindrical form and is disposed coaxially within the envelope 1 with a tubular heat shield 5 coaxially surrounding and electricallyconnected-to it, the heat shield 5 being of uniform diameter "Ice over the major part of its length, but narrowing in diameter towards its end nearer the anode 4. At this end the heat shield 5 carries a disc-shaped metal baflle 6 which is supported from the heat shield 5 by means of metal brackets 7 so that the baflle 6 is disposed just within the heat shield 5, with the axis of the envelope 1 passing perpendicularly through its centre.

The cathode heater 8 is housed within the body of the cathode 4 and is in the form of a wire helix, one end of which is connected to the cathode 4, and the other end of which is connected to a metal rod 9 which is sealed through the nearer end of the envelope 1 and serves as a connector for the heater 8.

The heat shield, cathode, heater, baflle assembly 2, 5, 6, 7, 8 is mounted on a support member 10 in the form of an inverted shallow metal cup, the member 10, in turn, being mounted on a second metal rod 11 which is sealed through the nearer end of the envelope 1 and serves as a second connector for the heater 8 and as a connector for the cathode 2.

At its end further from the cathode 2, the envelope 1 is provided with a reentrant portion 12 through which is sealed, coaxial with the envelope 1, an assembly including a glass tube 13 and a tungsten rod 14, the rod 14 being disposed coaxially within the tube 13. The outer end of the tube 13 is sealed onto the rod 14 at a point near the outer end of the rod 14 while the tube 13 is sealed through the portion 12 of the envelope 1 at a point about a third of the way along the length of the tube 13 from its inner end. The inner end of the rod 14 projects a short distance beyond the inner end of the tube 13, the projecting portion of the rod constituting the anode 4 of the device whilst the remainder of the rod 14 constitutes a connector for the anode 4. The projecting portion of the rod 14 is coaxially surrounded by a short metal tube 15 which is of the same internal diameter as the tube 13, but of slightly smaller wall thickness. The metal tube 15 is secured to the adjacent end of the tube 13 with the aid of a flanged metal collar 16 which is sealed around the metal tube 15 and has its flange sealed to a corresponding flange formed on a further metal collar 43 which is clamped around the tube 13. The length of the metal tube 15 is such that its inner end projects slightly beyond the inner end of the rod 14.

The control electrode arrangement 3 comprises three similar disc-shaped metal members 17 which are bolted together in parallel spaced apart relationship so as to be electrically insulated from one another, and are disposed between the anode and cathode in planes perpendicular to the axis of the envelope 1. Each member 17 has a small circular aperture 18 formed in it centrally through which the discharge between the cathode 2 and the anode passes in operation, the apertures 18 being of equal size and in register.

To support the control electrode arrangement the outer face of the member 17 nearest the anode 4 is sealed to the face of a flange formed at one end of a flanged metal collar 19 which is secured around the inner end of the metal tube 15.

.The three members 17 are respectively connected via three leads 20 to the inner ends of three metal rods 21 which are sealed through the side wall of the envelope 1 and serve as connectors for the control electrode arrangement 3. p

Referring now to FIGURES l and 3, in a typical application of the thyratron described above a high voltage derived from a bank of capacitors 22 is appliedbetween the anode 4 and the cathode 2, and the two outer members 17 of the control electrode arrangement 3 are connected to the cathode 2. The central member 17 of the control electrode arrangement 3 is utilized for triggering the thyratron and also for the application of a negative bias potential to reduce the recovery time of the thyratron. To this end the central member 17 is connected via a resistor 23 and the secondary winding 24 of a transformer 25 to the negative terminal of a suitable voltage source 26 whose positive terminal is connected to the cathode 2, the primary winding 27 of the transformer 25 being connected across a pulse voltage source 28.

In operation the thyratron is fired by application of a suitable positive-going voltage pulse to the central control electrode member 17 via the transformer 25, the discharge thus initiated ceasing on discharge of the capacitor bank 22.

As indicated above, to reduce the recovery time of the thyratron, the central control electrode member 17 is biassed negatively with respect to the cathode 2. The magnitude of this bias potential will be less than the magnitude of the voltage of the voltage source 26 by an amount equal to any voltage drop occurring across the resistor 23. More rapid recovery can thus be achieved with any particular biassing arrangement by reducing the current drawn from the voltage source 26.

With the thyratron described by way of example, owing to the presence of the outer control electrode members 17, only that region of the surface of the central member 17 immediately adjacent the aperture 18 in the central member 17 is exposed to the discharge; as a result the ion current collected by the central member 17 is small compared with that collected by the outer members 17, and hence much smaller than if the outer members 17 were absent. The application of the negative blessing potential to the central member 17 only, however, is found to achieve adequately short recovery time.

The control electrode member 17 between the anode 4 and the central control electrode member 17 also acts as an electrostatic screen thus reducing the capacitance between the anode 4 and the central member 17; the current induced in the central member 17 and the associated circuit as the capacitor bank 22 recharges is thus reduced.

Hence the current drawn from the voltage source 26 is much smaller than would be the case in the absence of the outer control electrode members 17 with a consequent reduction in recovery time.

Referring now to FIGURE 2, the second device to be described is a hydrogen-filled thyratron having a sealed hollow cylindrical glass envelope 29 in which is mounted an electrode structure including an indirectly heated cathode 30, a control electrode arrangement 31 and an anode 32.

The cathode 30 is of hollow cylindrical form and is disposed coaxially within the envelope 29 with two tubular heat shields 33 and 34 of difierent diameters coaxially surrounding it, the heat shields 33 and 34 being electrically connected to the cathode 30. At its end nearer the anode 32 the inner heat shield 33 carries a disc-shaped metal bafile 35, the battle being supported by brackets 36 at a position a short distance from the end of the cathode 30 nearer the anode 32 and the corresponding end of the heat shield 33 with the axis of the envelope 29 passing perpendicularly through its centre.

The cathode heater 37 is housed within the cathode 30 and is in the form of a wire helix, one end of which is connected to the cathode 30 and the other end of which is connected to a metal rod 38 which is sealed through the nearer end of the envelope 29 and serves as a connector for the heater 37.

The heat shield, cathode, heater, bafile assembly 30, 33, 34, 35, 36, 37 is mounted on a metal support member 57 which is in the form of a shallow inverted metal cup, the member 57, in turn, being mounted on a metal rod 39 which is sealed through the nearer end of the envelope 29 and serves as a second connector for the heater 37 and as a connector for the ca hede 30.

The control electrode arrangement 31 comprises three similar disc-shaped metal members 40 disposed between the anode 32 and the cathode 30 in parallel spaced apart relation in planes perpendicular to the axis of the envelope 29. Each member 40 has formed through it a rectangular aperture 41 through which the discharge between the anode 32 and the cathode 30 passes in operation, the apertures 41 all being of the same size and in register. The member 40 nearest the anode 32 is joined at its outer edge to one end of a tubular metal member 42, which is disposed coaxially within the envelope 29 and extends away from the anode 32 to a plane about halfway between the control electrode 31 and the cathode 30.

The three members 40 are respectively connected via three leads 55 to the inner ends of three metal rods 56 which are sealed through the side wall of the envelope 29 and serve as connectors for the members 40.

The member 40 nearest the cathode 30 carries a further disc-shaped metal baflle 44, the baflle being disposed between the control electrode 31 and the baffle 35, near the control electrode 31, in a plane perpendicular to the axis of the envelope 29, so as to lie in the direct path between the apertures 40 and the cathode 30.

The anode 32 is in the form of a hollow cylindrical metal box, the axis of the envelope 29 passing perpendicularly through the centres of the Hat faces of the box. The anode 32 is supported on the end of a metal rod 45 which is sealed through the nearer end of the enevlope 29 and serves as a connector for the anode 32.

In operation, the thyratron may suitably be used in a circuit arrangement similar to that described with reference to FIGURE 3, the presence of the outer control electrode members 40 being found to reduce the current drain on the negative biassing potential source, as is the case with the device described with reference to FIG- URE 1.

The tubular member 42 is included to reduce the possibility of long-path breakdown in operation.

Referring now to FIGURE 4, to reduce recovery time the control electrode arrangement 31 of the device described with reference to FIGURE 2 may be modified so as to comprise three parallel spaced-apart apertured members 46, 47 and 48 in which the central member is relatively thick and comprises an annular metal ring 49 sandwiched between two relatively thin apertured metal discs 50, the apertures in the discs 50 being smaller than the aperture in the ring 49, and not in register with one another so that the discharge follows an indirect path through the member 47. The two outer members 46 and 48 are each disc-shaped and the apertures in them are of the same size and respectively in register with the apertures in the nearer metal discs 50. With this design relatively good recovery time but somewhat greater current drain on the negative bias source is obtained compared with the more open design of control electrode described above with reference to FIGURE 2.

Referring now to FIGURE 5, in a second modified arrangement, also comprising three parallel spaced-apart members 51, 52 and 53, the member 51 nearest the anode is of substantially the same form as the central member 47 in the first modified arrangement described above, and the other two members 52 and 53 are each in the form of relatively thin apertured discs whose apertures are of the same size and each in register with the aperture in the nearer disc 54 forming part of the member 51. With this design recovery times about midway between those obtamed with the two designs described above are obtained and the current drain on the negative bias supply is about the same as that obtained with the more open design of control electrode described above with reference to FIG- URE 2.

It will be understood that, with all the devices described above, the triggering potential need not necessarily be applied to the central control electrode member 17, 40, 47 or 52 but y be P d o i her or both of the outer members 17, 40, 46, 48, 51 or 53. The negative biassing potential should, or" course, be always applied to the central member 17, 40, 47 or 52 for the current drain on the bias source is to be kept to a minimum.

We claim:

1. In an electric discharge device having a gas-filled envelope in which is housed an electrode structure comprising an anode, a cathode, a further metal electrode of planar form having at least one aperture through which the discharge between the anode and the cathode passes in operation, and means wereby a potential negative with respect to the cathode may be applied to said further electrode to reduce the recovery time of the gap between the anode and the cathode, that improvemen comprising: two planar metal members which are insulated from said further electrode and are disposed parallel to and adjacent the further electrode, one on the the anode side of the further electrode and the other on the cathode side of the further electrode, each said planar member having at least one aperture through which the discharge between said anode and cathode passes in operation, each aperture in the further electrode being in register with a said aperture in each said planar member, and the spacings of said planar members from said further electrode being sufiiciently small to limit the surface of said further electrode which is exposed to the discharge which passes between the anode and cathode in operation to each region immediately adjacent each aperture in said further electrode.

2. A device according to claim 1 wherein said further electrode and said planar metal members each have a single aperture through which the discharge between the anode and cathode passes in operation, said apertures being all in register.

3. A device according to claim 1 wherein said further electrode is relatively thick compared with said planar metal members and comprises an annular metal ring sandwiched between two relatively thin metal discs each having a single aperture, the apertures in the discs being smaller than the aperture in said ring and not in register with one another so that the discharge between the anode and the cathode follows an indirect path through the futrher electrode, and each of said planar metal members has a single aperture which is of the same size as, and is disposed in register with, the aperture in the nearer said disc.

4. A device according to claim 1 wherein said planar metal member that is nearer the anode is relatively thick compared with said further electrode and the other said planar metal member and comprises an annular metal ring sandwiched between two relatively thin metal discs each having a single aperture, the apertures in the discs being smaller than the aperture in said ring and not in register with one another so that the discharge between the anode and the cathode follows an indirect path through that planar metal member, and each of said other planar metal member and said further electrode has a single aperture which is of the same size and is disposed in register with the aperture in the nearer said disc.

5. A circuit arrangement comprising: an electric discharge device according to claim 1; means for applying a voltage between the anode and the cathode, means for applying a triggering potential to at least one of said further electrode and said planar metal members, means for maintaining said planar metal members at potentials positive with respect to said further electrode at least during periods immediately following the interruption of a discharge between the anode and the cathode, and means for maintaining said further electrode at a potential negative with respect to the cathode at least during periods immediately following the interruption of a discharge between the anode and the cathode.

6. A circuit arrangement according to claim 5 wherein the triggering potential is applied to said further electrode and said planar metal members are both maintained at the same potential as the cathode.

References Cited UNITED STATES PATENTS 2,486,134 10/1949 Elder 313 2,797,348 6/1957 Watrous 313200 X 2,877,372 3/1959 Palmer 313199 X 2,942,136 6/1960 Cook et al. 313-195 X 2,948,825 8/1960 Riley et al. 313--197 X 3,051,863 8/1962 Knight 313-197 X FOREIGN PATENTS 838,799 6/ 1960 Great Britain. 966,501 8/1964 Great Britain.

JOHN W. HUCKERT, Primary Examiner A. J. JAMES, Assistant Examiner US. Cl. X.R. 313167, 189, 1'94, 196, 204; 315-408 

